Process for the continuous spinning and stretching of zein filaments



Patented July 12, 1949 2,475,010 rnocass FOR 'rrm CONTINUOUS srnmma AND s'ma'rcnma or zam mama's Edward Terry Cline, Wilm to E. I. du Pont de Nemours mington, Del., a corporation of No Drawing.

4 Claims.

This invention relates to the production of shaped structures from zein and more particularly to a process for the production of zein synthetic fibers and the like.

In copending application Serial No. 517,854, now Patent No. 2,429,214,-a process is described and claimed wherein an aqueous alkaline solution of a prolamine including zein is extruded into an aqueous coagulating bath containing formaldehyde, a strong mineral acid and a watersoluble metal sulfate. However, zein filaments freshly formed by the procedure used in the said application, by'reason of their plastic nature and tendency to stick-together, do not lend themselves readily to stretching in a continuous process. It is necessary to interrupt the spinning operation in order to harden the filaments so that they may withstand the stretching procedure. Sufllclent hardening is obtained readily by contacting the prolamine filaments with an aqueous solution containing certain protein tanning agents and water-soluble inorganic salts. Hardening may be completed after stretching. The prolamine filaments so formed have dry and wet tenacities of at least 1.2 and 0.6 grams per denier, respectively. Since the prolamine filaments having these properties are useful in the manufacture of'iabrics, the provision of a continuous process for spinning and stretching zein fibers which are substantially free from the undesirable property of sticking together after coagulation is highly desirable.

This invention has as an object the conversion of zein into shaped structures, particularly filaments, fibers, yarns and threads. A, still further object is to provide a continuous process for spinning and stretching zein fibers which are substantially free from the undesirable property of sticking together after coagulation. Additional objects will appear hereinafter.

These and other objects and advantages are accomplished by the hereindescribed invention which comprises continuously extruding an aqueous zein solution containing from 12% to 18% zein by weight, from 1.5% to 3.0% sodium hydroxide based on the weight of the zein and about 5% formaldehyde based on the weight of the zein, into an aqueous coagulating bath having a temperature within the range of from 30 to '10 c. and containing from 0.5% to 10.0% by weight of formaldehyde, from 11% to 15% by weight of sulfuric acid, at least by weight of sodium or zinc sulfate, and an amount within cation-active surface-active agent, removing the Application February I. Serial No.'646,710

ington, Del., illignor.

& Company, Wil- Delaware z the range of from 0.01% to 0.5% by weight of a 2 resultant formed zein filaments from the bath. stretching the zein filaments an amount within the range of from 50% to of their maximum draw ratio in an aqueous sodium sulfate solution having a temperature within the range of from 70 to 110 C. and containing from 10% to 30% by weight of sodium sulfate and an amount within the range of from 0.01% to 0.5% by weight of a cation-active surface-active agent, and then immersing the resultant stretched filaments in an aqueous formaldehyde hardening solution having a pH of not more than about 8 and containing at least 10% by weight of salt material selected from the group consistingof water-soluble inorganic salts and admixtures of said salts.

By the term "fibers and the like," as used herein and in .the appended claims is .meant filaments, fibers, yarns and threads of any denier or crosssectional shape and bands or tows consisting of any number of such filamentary articles.

By the expression "water-soluble as used herein and in the appended claims is meant a compound which is soluble in water to the extent of at least 5 grams per cubic centimeters of water at 20 C.

By the term "inorganic salt" as used herein and in the appended claims is meant a salt of a metal and an inorganic acid.

, The maximum draw ratio of a fiber and the like which is being stretched between rotating rollers is the ratio between the peripheral speed of the faster roller and the peripheral speed of the slower roller when the rollers are operating at such speeds that the fiber is being stretched to a point Just below that at which it will break.

By the term "neutral salt as employed herein and in the appended claims is meant a salt which, when dissolved in water, provides a solution having a pH of about 7, while by the expression "acid-reacting Salif'is meant a salt which, when dissolved in water, produces a solution having a pH ofiess than '7. t v

Tenacities' andfelongations of multifilament yarns are given in terms of measurements made with a constant specimen-rate-of-load type testingmachine (Scott incline plane tester Model tened in the carriage clamp located four inches from the left-hand clamp. The other end of the,

yarn is then passed through the left-hand clamp and over the roller on the tension device. Bum- 3 to the yarn end to balance left-hand clamp is started and allowed cient tension is applied the tension device and the fastened. The machine is to trace a stress-strain curve for the yarn on the chart provided. When the yarn breaks, a mark is made on the chart showing the position of the pen at the time of break. From the location of the point, the tenacity and elongation of the specimen may be read on the chart. Tenacities are based on original yarn dimensions. when tested similarly on this machine, a sample of recent, 200 denier, 35 filament, 3 twist, textile grade, oiled, viscose rayon is found to have tenacities of 1.9, 0.9 and 1.6 grams per denier and elongations of 24%, 26% and 16%, dry, wet and loop, respectively, at 60% relative humidity and 21 C.

By the term "cation-active surface-active agent as employed herein and in the appended claims is meant an organic compound or admixture of organic compounds which, in aqueous systems, dissociate to yield positively charged surface-active cations. Compounds which are particularly adapted for this purpose are quaternary ammonium, quaternary phosphonium and tertiary sulfonium compounds which contain a positively charged ion that contains an aliphatic hydrocarbon group having at least six carbon atoms. Examples of such compounds are disclosed, for instance, in U. S. Patent No. 2,123,740.

In the process of this invention, the preparation of the spinning solution is accomplished by agitating the zein with the required amount of water and formaldehyde for several minutes. A small amount of sodium pentachlorophenolate is advantageously added to the spinning solution to act as a mold inhibitor in the finished fibers and the like. Then, the alkali in the form of a aqueous solution .of sodium hydroxide is added with thorough agitation. The solution becomes homogeneous in about thirty minutes at room temperature. Homogeneity is accomplished in a shorter time if the solution is continuously agitated. Before spinning, it is customary to filter the solution and deaerate it under vacuum to avoid stoppages in the spinneret and discontinuity in the spinning. In order to avoid extensive alkali degradation of the zein, it is preferred to spin as soon as possible after the solution becomes homogeneous.

In the process of this invention, the usual gear pump, candle filter and viscose type spinneret are satisfactory for use. The number of orifices in the spinneret has little effect, except on the rate of fiber production, so that spinnerets containing either one or a multiplicity of orifices may be used. From the spinneret, the solution is extruded directly into a coagulating bath containing chemicalswhich facilitate the transformation of the solution from a liquid to a solid fiber. A suitable bath may be described as one having a density greater than 1.1 and containing a high percentage of water-soluble inorganic salts or mixtures thereof, such as sodium sulfate or sodium chloride, from 11% to 15% sulfuric acid, formaldehyde, and a small amount of a cation-active surface-active agent.

The filaments are then stretched to at least 50% of their maximum draw ratio in a concentrated aqueous solution of a water-soluble inorganic salt at a temperature above 50 C. and the stretched fibers are passed into a final hardening bath containing formaldehyde and water-soluble inorganic salts.

The following examples are given for illustrative purposes and are not intended to place any in terms of anhydrous rather than hydrated weight.

Example I A spinning solution containing 15.2% dry zein. 0.76% formaldehyde, 0.29% sodium hydroxide and 0.15% sodium pentachlorophenolate (all perzein with the necessary amount of water, form dehyde and sodium pentachlorophenate for several minutes and adding the sodium hydroxide in the form of a 10% aqueous solution with thorough agitation. In about thirty minutes at room temperature with agitation, the solution becomes homogeneous. It is then filtered at 20 to 60 pounds gauge pressure through an assembly of filter cloth and wire screen. The filtrate is centrifuged to aid in removing air bubbles. The time required for centrifuging varies with the amount of air introduced during filtration and with the viscosity of the solution. For this composition, a half hour at 1,500 B. P. .M. has been found sufllcient. Deaeration of thesolution is completed by subjecting it to reduced pressure at about 0.5 pound per square inch absolute for one hour. At this point, the composition has a viscosity of about 37 poises at 26 C. and a pH of 11.3 as measured with a high pH glass electrode.

The solution is cooled to 10 to 15 C. and thereafter maintained in this temperature range. It is spun in ordinary viscose spinning apparatus. The solution' is fed under 20 pounds per square inch gauge pressure to a gear pump which forces it at a rate of 3.9 cc. per minute through a candle filter and spinneret into the coagulating bath. That portion of the apparatus between the spinneret and the candle filter which is in contact with the hot coagulating bath is jacketed with water at about 13 C. to prevent premature warming of the spinning solution. The spinneret has sixty orifices, each of which has a diameter of about 0.0035 inch. The coagulating bath contains 11.3% sulfuric acid, 20.3% sodium sulfate,

3.6% zinc sulfate, 2.7% formaldehyde and 0.05% trimethyloctadecylammonium bromide and is maintained at a temperature of 50 C. In the coagulating bath, the filaments issuing from the spinneret are converged into a yarn and are passed around twelve rollers or pulleys, each of which has a circumference of 8.1 cm. in the groove, 'six of which are mounted at each end of the coagulating bath in such a manner that they are free to rotate about vertical shafts. The length of yarn travel in the coagulating bath is of the order of 400 inches. From the last roller, the yarn is led directly to a six inch-diameter, glass godet wheel operated at 53 R. P. M. The godet wheel is fitted with an idler roller such that several wraps may be taken around the wheel to prevent yarn slippage.

From the godet wheel, the yarn is led under a roller immersed in a solution containing 30% sodium sulfate and 0.05% trimethyloctadecylammonium bromide, the solution being heated at 101 C., and then directly to the wind-up bobbin.

The length of yarn travel in this hot salt bath is of the order of sixteen inches. The wind-up bobbin is operated at a peripheral speed Of 1,680 inches per minutes, such that the yarn is stretched 68% during passage through the hot salt bath.

up bobbin, it is sprayed with 20% sodium chloride solution to keep it moist. when suillcient yarn is wound on the bobbin, the bobbin is removed from the wind-up machine and the yarn is re-. wound into the form of a skein. The skein is immersed in a solution containing 28% sodium chloride, 2% hydrochloric acid and 1% formaldehide at 40 C. for seventeen-hours. The skein is then well washed in running water and allowed to dry. when dry, the yarn is twisted two turns per inch on a ring twister.

The 60-i'ilament yarn thus prepared is free of stuck filaments. It has a denier of 164, tenacities of 0.91, 0.53 and 0.73 gr-am perv denier dry, wet and loop. respectively, and elongations of 12%, 15% and 6% dry, wet and loop, respectively, when tested on at Scott incline plane tester at 60% relative humidity and 21 C. The yarn has a shrinkage in boiling water of 4% When similarly tested, a 1/32s (250 denier) 62's quality, worsted (wool) yarn had tenacities of 0.64 and 0.46 gram per denier dry and wet, respectively, and elongations of 14% and 39% dry and wet, respectively.

Zein yarns similarly spun except for the use of less than 11% sulfuric acid, in the coagulating bath, by reason of their plastic nature and tendency to stick together did not lend themselves satisfactorily to stretching in the hot salt bath between the godet wheel and the wind-up bobbin in the continuous process. To avoid fused and stuck filaments, it was necessary to interrupt the process and partially harden such filaments over 'a period of time in a, separate hardening bath prior to stretching.

Example I! The spinning solution described in Example I was spun in the same manner as that described in Example I except that the coagulating bath contained 14.6% sulfuric acid, 19.1% sodium sulfate, 3.5% zinc sulfate, 2.6% formaldehyde and 0.05% trimethyloctadecylammonium bromide. The yarn thus prepared was likewise free of stuck filaments. It had a denier of 166, tenacities of 0.91, 0.49 and 0.75 gram per denier dry, wet and loop, respectively, and elongations of 11%, 14% and 7% dry, wet and loop, respectively.

It is to be understood that the hereinbefore disclosed specific embodiments of this invention may be subject to variation and modification without departing from the scope thereof. However, it is necesary in accomplishing the process of this invention to carry out the following steps:

(1) The filaments are spun from an aqueous alkaline zein solution containing from 12% to 18% of the zein and having a pH'of at least 8;

(2) The coagulation is effected by extruding the zein solution into an aqueous bath. containing formaldehyde, from 11% to 15% by weight of sulfuric acid and at least by weight of a salt material selected from the group consisting Of water-soluble inorganic salts and admixtures of said salts;

(3) The coagulated filaments are stretched at least 50% of their maximum draw ratio in a concentrated aqueous solution of a saltmaterial selected from the group consisting of watersoluble neutral and acid-reacting inorganic salts and admixtures of said salts, said solution having a temperature of more than 70 C.;

(4) The stretched fibers are finally hardened in an aqueous formaldehyde hardening bath having a pH of less than 8 and containing at least 10% by weight of salt material selected from the group consisting of water-soluble sodium hydroxide content, based on the zein, it

' is from 1.5% to 3.0%.

It is to be understood that in addition to zein and sodium hydroxide, the spinning solution may contain a small percentage of formaldehyde, for instance from 1% to 10% formaldehyde based on the weight of the zein. Zein fibers and the like having optimum properties are obtained when said solution contains about 5% formaldehyde based on'the weight. of the zein and for this reason, the use of spinning solutions containing about this amount of formaldehyde are preferred.

7 When coagulating baths of the type described in Examples I and II are used except that the baths contain sulfuric acid in concentrations of 3.9%, 5.8% and 7.7%, respectively, sticking of the zein filaments is encountered during the stretching operation when it is carried out immediately after coagulation as in a continuous spinning and stretching process. When the sulfuric acid concontration in the coagulating bath is 11.3% and 14.6%respectively, the fibers may be spun and stretched continuously without difllculty and the filaments arecompletely free from sticking during the stretching operation. In baths containing sulfuric acid in a concentration as high as 9.7%, 4% to 5% sodium sulfate, 14% zinc sulfate, 3% formaldehyde and a small amount of a surface-active agent, filament sticking is still encountered, whereas at 11.4% or 13% sulfuric acid, the filaments are completely free from sticking. At acidities of 2%, 4% or 6%, the zein yarn in the coagulating bath is so plastic that it cannot be satisfactorily stretched. Zein yarns free from stuck filaments have been obtained using coagulating baths containing 11.9% sulfuric acid, 15% sodium sulfate, 15% zinc sulfate, 3% formaldehyde and a small amount of surface-active agent whereas at an acid concentration of 10%, the yarn was wiry as a result of stuck filaments.

The coagulating bath should contain a high percentage of a water-soluble inorganic salt or admixture of water-soluble inorganic salts. The minimum salt content necessary is of the order of about 10% by weight While the upper limit is determined by the solubility of the inorganic salts in the coagulating bath composition. While any water-soluble inorganic salt is adapted for use in the coagulating bath, water-soluble metal sulfates provide superior coagulating baths and hence are preferred. Examples of said metal sulfates include aluminum, aluminum potassium, aluminum sodium, magnesium, potassium, sodium and zinc sulfates. The salts which are most readily available and which provide most satisfactory coagulating baths are the sulfates of sodium, zinc and aluminum.

Coagulating bath temperatures of 20 to. C. may be used. However, it is preferred to use temperatures within the range of 30 C. to 70 C. since optimum filament properties result when temperatures within this range are employed. If too low temperatures are used, fiber properties anasvo solutions containing no sodium dodecyl sulfate and do not require cooling during the spinning operation.

The coagulated filaments are subjected to stretching in a hot concentrated aqueous solution of a water-soluble neutral or acid-reacting salt of a mineral acid or admixture of said salts. While any water-soluble salt of a mineral acid -which, in water, provides a solution having a pH of'not more than about '7, e. g., aluminum sulfate, zinc sulfate, ammonium sulfate, is adapted for use in the stretching bath, it is preferred, on account of the superior fibers formed therewith, to employ a stretching bath comprising .a

sodium salt of a strong mineral acid or admixture of said salts. Sodium chloride and sodium sulfate provide fibers and the like having most desirable properties and are therefore preferred salts. The use of alkaline-reacting salts, especially the strong alkaline salts, is to be avoided, but the stretching bath may contain water-soluble salts of organic acids, e. g.; sodium acetate-and potassium i'ormate, if desired. Generally, the salt concentration should be above and the temperature above 50 C. Preferred salt concentrations lie within the range of from to 30% and temperatures within the range of from 70 to 110 C. Temperatures in excess of 50 C. are necessary in order to obtain appreciable stretching. In the stretching step, other things being equal, higher degrees of stretch generally result in higher dry and wet tenacities in the final product. However, excessively high degrees of stretch cause frequent yarn and filament breakage. The preferred amount of stretch for a typical yarn is within the range of from 50% to 90% of the maximum draw ratio.

After the filaments have been coagulated and stretched, they are given a final hardening treatment and then washed. Washing may be accomplished by immersing the filaments in the form of a hank in circulating water. formaldehyde insolubilization of the filament may be effected in any known manner by contacting said filaments with an aqueous solution of formaldehyde containing at least 10% by weight of a water-soluble inorganic salt or admixture of said salts and having a pH of less than 8. For optimum results said aqueous solution should contain at least 1% formaldehyde by weight.

After the final hardening treatment, the fibers and the like may be washed either under tension or in a relaxed condition until substantially free of acid and salts and then dried by methods well known to the art.

In order that the filaments have high resistance to hot dilute acid baths such as are encountered in dyeing and to other hot aqueous systems, further treatmentof the filaments with formaldehyde at elevated temperatures may be used. Additional treatments may be applied if desired, including treatments to neutralize excess acid or The final alkali, treatments to prevent shrinkage and loss of orientation, treatments with softening agents, and treatments with oils or sizes to assist in weaving.

If desired, the fibers can be set before the final hardening step by treatment at an elevated temperature in a medium which has little swelling action on the fibers.

The preparation of zein fibers and the like differs from that of casein, soya protein and peanut protein fibers in that optimum spinning behavior and fiber properties are attained at a much higher level of acidity in the coagulating bath. Thus, as described elsewhere in this specification, continuous spinning and stretching of zein fibers and optimum fiber properties result when the acidity of the formaldehyde-containing coagulating bath is in the range of 11% to 15% sulfuric acid. On the other hand, best results in terms of continuous spinning and stretching behavior and of final fiber properties are obtainfibers is hereby made possible. Prior to this invention, no satisfactory process for accomplishing this result was known.

The fibers prepared by the process of this invention are useful in the manufacture of textile materials, for example, in fabrics used for dresses and suits.

As many apparently different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

Iclaim:

1. In a continuous process for obtaining zein synthetic fibers and the like, the steps of extruding an aqueous alkaline solution of zein into an aqueous coagulating bath containing at least 0.5% formaldehyde; from 11% to 15% by weight a of sulfuric acid; and salt material selected from the group consisting of water-soluble inorganic salts and admixtures of said salts, contacting the resultant formed zein filaments with said bath for a time sufiicient to effect partial hardening, removing the resultant formed, partially hardened zein filaments from the coagulating bath, stretching the resultant formed, partially hardened filaments at least 50% of their maximum draw ratio in a concentrated aqueous solution of salt material selected from the group consisting of water-soluble neutral and acid-reacting salts of mineral acids and admixtures of said salts, said solution having a temperature of more than 50 .C. and thEIL immersing the resultant stretched, partially hardened filaments in an aqueous formaldehyde hardening solution.

2. In a continuous process for obtaining zein synthetic fibers and the like, the steps of admixing zein and an alkali with water in such proportions as to provide a solution containing from 12% to 18% by weight of zein and having a pH of at least 9, extruding the resultant aqueous arrears alkaline zein solution into an aqueous coagulating bath containing at least 0.5% formaldehyde, from 11% to 15% by weight of sulfuric acid and at least 10% by weight of salt material selected from the group consisting of water-soluble inorganic salts and admixtures of said salts, contacting the resultant formed zein filaments with said bath for a time suflicient to eifect partial hardening, removing the resultantformed, partially hardened zein filaments from the coagulating bath, stretching the resultant formed, partially hardened filaments at least 50% of their maximum draw ratio in an aqueous salt solution having a temperature above 50 C. and containing at least by weight of salt material selected from the group consisting of water-soluble neutral and acid-reacting salts of mineral acids and admixtures of said salts, and then immersing the resultant stretched, partially hardened filaments in an aqueous formaldehyde hardening solution having a pH of less than 8 and containing at least 10% by weight of salt material selected from the group consisting of water-soluble inorganic salts and admixtures of said salts.

3. In a continuous process for obtaining zein synthetic fibers and the like, the steps of extruding an aqueous'sodium hydroxide solution of -zein, said solution containing from 12% to 18% by weight of zein, sodium hydroxide within the range of from 1.5% to 3.0% sodium hydroxide based on the weight of the zein and a small amount of formaldehyde, into an aqueous coagulating bath having a temperature within the range of from C. to 70 C. and containing from 0.5% to 10% by weight of formaldehyde,

from 11% to 15% by weight of sulfuric acid, at-

least 10% by weight of a water-soluble metal sulfate and up to 1%, by weight of a cation-active surface-active agent. contacting the resultant formed Iein filaments with said bath for a time suillclent to eifect partial hardening, removing the resultant formed, partially hardened zein fllaments from the coagulating bath; stretching the resultant formed, partially hardened filaments at least of their maximum draw ratio in an aqueous salt solution having a temperature above 50 C. and containing from 10% to by weight acid and immersing the resultant stretched, partially hardened filaments .in an aqueous formaldehyde hardening solution having a pH of not more than 8 and containing at least 10% by weight of salt material selected from the group consisting of water-soluble inorganic salts and admixtures of said salts.

4. In a continuous process for obtaining zein synthetic fibers and the like, the steps of extruding an aqueous zein solution containing from 12% to 18% by weight of zein, and about 5% formaldehyde and sodium hydroxide within the range 'of 1.5% to 3% based on the weight of the zein, into an aqueous coagulating bath having a temperature within the range of from 30 C. to 70 C. and containing from 0.5% to 10% by weight of formaldehyde, from 11% to 15% by weight of sulfuric acid, at least 10% by weight of sodium sulfate, and from 0.1% to 0.5% by weight of a cation-active surface-active agent, contacting the resultant formed zein filaments with said bath for a time sufficient to effect partial hardening, removing the resultant formed, partially hardened zein filaments from the coagulating bath, stretching the resultant formed, partially hardened filaments at least 50% of their maximum draw ratio in an aqueous sodium sulfate solution having a temperature within the range of from 70 C. to C. and-containing *from 10% to 30% by weight of sodium sulfate and then immersing the resultant stretched, partial- 1y hardened filaments in an aqueous formaldehyde hardening solution having a pH of not more than about 8 and containing at least 10% by weight of a salt material selected from the group consisting of water-soluble inorganic salts and admixtures of said salts.

, EDWARD TERRY CLINE.

REFEanNcEs crrnn The following references are of record in the file of this patent: 

